These medical devices typically comprise a housing that is generally designated a “generator”, which is electrically and mechanically connected to one or more other devices known as “leads”. Leads are provided with electrodes that are intended to come into contact with the patient's tissues at sites to stimulate (i.e., deliver electrical pulses to the tissues) and/or at which it is desired to collect (i.e., sense, detect) an electrical signal. Such sites include, but are not limited to a patient's myocardium, nerve, or muscle tissue. In the case of a diagnostic and therapeutic cardiac device, the electrodes can be endocardial electrodes (e.g., placed in a cavity of the myocardium in contact with the wall thereof), epicardial electrodes (used in particular to define a reference potential, or for application of a shock pulse used for defibrillation), or intravascular electrodes (for example, the lead is introduced into the coronary sinus to a location facing the wall of the left ventricle).
One aspect of the development of these devices is the increasing number of electrodes employed in a lead, especially for those devices known as “multisite” devices that allow selection of the stimulation/detection sites for optimization of the operation of the device.
Thus, in the particular case of implantable devices used for ventricular resynchronization (which devices also are called cardiac resynchronization therapy (CRT) devices), a patient is implanted with a device having electrodes to stimulate either or both ventricles. The right ventricular pacing (and the right atrium pacing) is typically obtained using a conventional endocardial lead, but for the left ventricle the access is more complex; stimulation is generally performed using a lead that is inserted into the coronary sinus of the right ventricle and then pushed into a coronary vein on the epicardium, so that the end of the lead comes into contact with and against the left ventricle. This procedure is quite delicate, because the diameter of coronary vessels is reduced as the lead progresses, so it is not always easy to find the optimal position during implantation. In addition, the proximity of the phrenic nerve can sometimes lead to inappropriate stimuli.
To alleviate these difficulties, efforts were conducted to develop “multielectrode” leads, providing, for example, several electrodes among which the most effective stimulation electrode configuration can be tested and then chosen after implantation. One such lead is described for example in EP 1938861 A1 and its counterpart U.S. Pat. Publication No. 2008/0177343 A1 (both assigned to Sorin CRM S.A.S, previously known as ELA Medical).
To manage a multiplicity of electrodes, multiplexing systems for interfacing the various electrodes (and any sensors carried by the lead) have been developed with the two conductors traversing the lead and connected to the generator terminals. EP 2082684 A1 and its counterpart U.S. Pat. Publication No. 2009/0192572 A1 (both assigned to Sorin CRM S.A.S, previously known as ELA Medical) describe a generator connected to a multielectrode lead by two conductors associated with a multiplexor/demultiplexor circuit. The two conductors firstly ensure the collection of depolarization signals and the delivery of stimulation pulses, and secondly deliver the multiplexor/demultiplexor logic signals to control the selector switches of one or more electrodes of the lead. These signals also supply the required energy to the multiplexor/demultiplexor circuit and switches for their operation. Aforementioned EP 1938861 A1 and its counterpart U.S. Pat. Publication No. 2008/0177343 A1 describe such a multiplexor and controlled switching circuit, and a protocol for exchanging signals between the generator and the various multiplexors of the lead to ensure the desired switching by delivering trains of pulses on the specific two-wire line.
The U.S. Pat. Publication 2011/0029042 A1 describes another device comprising a controlled switch module of the same type, with a controlled switch associated with a memory component that stores a unique identifier used for addressing by the multiplexor/demultiplexor.
A first drawback of these known devices is the need to provide a permanent power supply to the circuits that allow the multiplexing of the switches defining the electrode configuration. This results in an increase in overall implant/lead system power consumption, which is detrimental to the autonomy (i.e., the useful life) of an implanted device.
Specifically, for a given multielectrode lead as described in the above two patent publication documents, the electrodes are selected by the generator via the two-wire link carried by the lead body, whose two poles are generally designated as “distal” and “proximal” poles. Note that in some cases, the link can include one or more additional conductors, and the connection may, for example, be a three wire connection incorporating an additional conductor for direct transmission to the generator of signals produced, for example, by an endocardial acceleration sensor located in the lead distal tip.
A circuit module, generally formed as a specific integrated ASIC circuit, is integrated at each electrode. This module, which must be supplied via the two-wire connection, receives the configuration data to define if the corresponding electrode has to be connected or not and, if so, to which pole, the distal or proximal one. The configuration data are interpreted by the module, which performs (or not) the connection of one or the other of the distal or proximal conductors to the selected electrode by means of controlled switches.
These controlled switches are generally volatile switches, usually MOS transistors or MEMS, which are easy to implement. However, once the various modules of the lead are configured to activate one or more stimulation sites corresponding to the respective electrodes, the electrode configuration must be continuously maintained for the collection of the cardiac signal and the delivery, if necessary, of stimulation pulses.
One drawback is the need to permanently or periodically provide sufficient energy (that is to say, at least throughout the period when the device is active) to supply the different modules of the lead. Another drawback is that for a given lead, it is necessary to use a specific implantable medical device which is dedicated to the particular lead. Indeed, the generator associated with the lead must be able to provide the appropriate signals to control the multiplexing and the energy to make and keep the lead functional. Yet another drawback is that in some cases the lead is no longer supplied with power by the generator, resulting in a loss of the pacing configuration, which must be reprogrammed. This is particularly true at the end of life of the implant (i.e., a low battery condition), during replacement of the original implantable device with a new implantable device: during surgery, the lead is de-energized and once the new implant able device is in place and coupled to energize the lead it is necessary to reconfigure the lead electrodes to their previous state—which in addition assumes that the previous state was saved while the old generator was still functional.